[Git][ghc/ghc][wip/rts-rm-c99-check] autoconf/ghc-toolchain: remove obsolete C99 check

30 Sep 2025


      Cheng Shao pushed to branch wip/rts-rm-c99-check at Glasgow Haskell Compiler / GHC


Commits:
3c9bcb37 by Cheng Shao at 2025-09-29T20:07:47+02:00
autoconf/ghc-toolchain: remove obsolete C99 check

This patch removes obsolete c99 check from autoconf/ghc-toolchain. For
all toolchain & platform combination we support, gnu11 or above is
already supported without any -std flag required, and our RTS already
required C11 quite a few years ago, so the C99 check is completely
pointless.

- - - - -


6 changed files:

- configure.ac
- distrib/configure.ac.in
- m4/fp_cmm_cpp_cmd_with_args.m4
- − m4/fp_set_cflags_c99.m4
- utils/ghc-toolchain/src/GHC/Toolchain/Tools/Cc.hs
- utils/ghc-toolchain/src/GHC/Toolchain/Tools/Cpp.hs


Changes:

=====================================
configure.ac
=====================================
@@ -448,11 +448,6 @@ AC_SUBST([CmmCPPCmd])
 AC_SUBST([CmmCPPArgs])
 AC_SUBST([CmmCPPSupportsG0])
 
-FP_SET_CFLAGS_C99([CC],[CFLAGS],[CPPFLAGS])
-FP_SET_CFLAGS_C99([CC_STAGE0],[CONF_CC_OPTS_STAGE0],[CONF_CPP_OPTS_STAGE0])
-FP_SET_CFLAGS_C99([CC],[CONF_CC_OPTS_STAGE1],[CONF_CPP_OPTS_STAGE1])
-FP_SET_CFLAGS_C99([CC],[CONF_CC_OPTS_STAGE2],[CONF_CPP_OPTS_STAGE2])
-
 dnl ** Do we have a compatible emsdk version?
 dnl --------------------------------------------------------------
 EMSDK_VERSION("3.1.20", "", "")


=====================================
distrib/configure.ac.in
=====================================
@@ -163,11 +163,6 @@ AC_SUBST([CmmCPPCmd])
 AC_SUBST([CmmCPPArgs])
 AC_SUBST([CmmCPPSupportsG0])
 
-FP_SET_CFLAGS_C99([CC],[CFLAGS],[CPPFLAGS])
-dnl FP_SET_CFLAGS_C99([CC_STAGE0],[CONF_CC_OPTS_STAGE0],[CONF_CPP_OPTS_STAGE0])
-FP_SET_CFLAGS_C99([CC],[CONF_CC_OPTS_STAGE1],[CONF_CPP_OPTS_STAGE1])
-FP_SET_CFLAGS_C99([CC],[CONF_CC_OPTS_STAGE2],[CONF_CPP_OPTS_STAGE2])
-
 dnl ** Which ld to use?
 dnl --------------------------------------------------------------
 FIND_LD([$target],[GccUseLdOpt])


=====================================
m4/fp_cmm_cpp_cmd_with_args.m4
=====================================
@@ -56,27 +56,6 @@ else
   AC_MSG_RESULT([no])
 fi
 
-AC_MSG_CHECKING([the C-- preprocessor for C99 support])
-cat > conftest.c <<EOF
-#include <stdio.h>
-#if !defined __STDC_VERSION__ || __STDC_VERSION__ < 199901L
-# error "Compiler does not advertise C99 conformance"
-#endif
-EOF
-if "$CMM_CPP_CMD" $CMM_CPP_ARGS conftest.c -o conftest -g0 >/dev/null 2>&1; then
-  AC_MSG_RESULT([yes])
-else
-    # Try -std=gnu99
-    if "$CMM_CPP_CMD" -std=gnu99 $CMM_CPP_ARGS conftest.c -o conftest -g0 >/dev/null 2>&1; then
-      $3="-std=gnu99 $$3"
-      AC_MSG_RESULT([needs -std=gnu99])
-    else
-      AC_MSG_ERROR([C99-compatible compiler needed])
-    fi
-fi
-rm -f conftest.c conftest.o conftest
-
-
 $2="$CMM_CPP_CMD"
 $3="$$3 $CMM_CPP_ARGS"
 
@@ -85,4 +64,3 @@ unset CMM_CPP_CMD
 unset CMM_CPP_ARGS
 
 ])
-


=====================================
m4/fp_set_cflags_c99.m4 deleted
=====================================
@@ -1,38 +0,0 @@
-# FP_SET_CFLAGS_C99
-# ----------------------------------
-# figure out which CFLAGS are needed to place the compiler into C99 mode
-# $1 is name of CC variable (unmodified)
-# $2 is name of CC flags variable (augmented if needed)
-# $3 is name of CPP flags variable (augmented if needed)
-AC_DEFUN([FP_SET_CFLAGS_C99],
-[
-    dnl save current state of AC_PROG_CC_C99
-    FP_COPY_SHELLVAR([CC],[fp_save_CC])
-    FP_COPY_SHELLVAR([CFLAGS],[fp_save_CFLAGS])
-    FP_COPY_SHELLVAR([CPPFLAGS],[fp_save_CPPFLAGS])
-    FP_COPY_SHELLVAR([ac_cv_prog_cc_c99],[fp_save_cc_c99])
-    dnl set local state
-    CC="$$1"
-    CFLAGS="$$2"
-    CPPFLAGS="$$3"
-    unset ac_cv_prog_cc_c99
-    dnl perform detection
-    AC_PROG_CC_C99
-    fp_cc_c99="$ac_cv_prog_cc_c99"
-    case "x$ac_cv_prog_cc_c99" in
-      x)   ;; # noop
-      xno) AC_MSG_ERROR([C99-compatible compiler needed]) ;;
-      *)   $2="$$2 $ac_cv_prog_cc_c99"
-           $3="$$3 $ac_cv_prog_cc_c99"
-           ;;
-    esac
-    dnl restore saved state
-    FP_COPY_SHELLVAR([fp_save_CC],[CC])
-    FP_COPY_SHELLVAR([fp_save_CFLAGS],[CFLAGS])
-    FP_COPY_SHELLVAR([fp_save_CPPFLAGS],[CPPFLAGS])
-    FP_COPY_SHELLVAR([fp_save_cc_c99],[ac_cv_prog_cc_c99])
-    dnl cleanup
-    unset fp_save_CC
-    unset fp_save_CFLAGS
-    unset fp_save_cc_c99
-])


=====================================
utils/ghc-toolchain/src/GHC/Toolchain/Tools/Cc.hs
=====================================
@@ -11,7 +11,6 @@ module GHC.Toolchain.Tools.Cc
     , compileC
     , compileAsm
     , addPlatformDepCcFlags
-    , checkC99Support
     ) where
 
 import Control.Monad
@@ -51,12 +50,8 @@ findCc archOs llvmTarget progOpt = do
     cc1 <- ignoreUnusedArgs cc0
     cc2 <- ccSupportsTarget archOs llvmTarget cc1
     checking "whether Cc works" $ checkCcWorks cc2
-    cc3 <- oneOf "cc doesn't support C99" $ map checkC99Support
-        [ cc2
-        , cc2 & _ccFlags %++ "-std=gnu99"
-        ]
-    checkCcSupportsExtraViaCFlags cc3
-    return cc3
+    checkCcSupportsExtraViaCFlags cc2
+    return cc2
 
 checkCcWorks :: Cc -> M ()
 checkCcWorks cc = withTempDir $ \dir -> do
@@ -88,17 +83,6 @@ ccSupportsTarget archOs target cc =
     checking "whether Cc supports --target" $
     supportsTarget archOs _ccProgram checkCcWorks target cc
 
-checkC99Support :: Cc -> M Cc
-checkC99Support cc = checking "for C99 support" $ withTempDir $ \dir -> do
-    let test_o = dir </> "test.o"
-    compileC cc test_o $ unlines
-        [ "#include <stdio.h>"
-        , "#if !defined __STDC_VERSION__ || __STDC_VERSION__ < 199901L"
-        , "# error \"Compiler does not advertise C99 conformance\""
-        , "#endif"
-        ]
-    return cc
-
 checkCcSupportsExtraViaCFlags :: Cc -> M ()
 checkCcSupportsExtraViaCFlags cc = checking "whether cc supports extra via-c flags" $ withTempDir $ \dir -> do
   let test_o = dir </> "test.o"


=====================================
utils/ghc-toolchain/src/GHC/Toolchain/Tools/Cpp.hs
=====================================
@@ -19,7 +19,7 @@ import GHC.Toolchain.Prelude
 import GHC.Toolchain.Program
 
 import GHC.Toolchain.Tools.Cc
-import GHC.Toolchain.Utils (withTempDir, oneOf, expectFileExists)
+import GHC.Toolchain.Utils (withTempDir, expectFileExists)
 
 newtype Cpp = Cpp { cppProgram :: Program
                     }
@@ -160,13 +160,7 @@ findJsCpp progOpt cc = checking "for JavaScript C preprocessor" $ do
 findCmmCpp :: ProgOpt -> Cc -> M CmmCpp
 findCmmCpp progOpt cc = checking "for a Cmm preprocessor" $ do
   -- Use the specified CPP or try to use the c compiler
-  foundCppProg <- findProgram "Cmm preprocessor" progOpt [] <|> pure (programFromOpt progOpt (prgPath $ ccProgram cc) [])
-  -- Check whether the C preprocessor needs -std=gnu99 (only very old toolchains need this)
-  Cc cpp <- oneOf "cc doesn't support C99" $ map checkC99Support
-        [ Cc foundCppProg
-        , Cc (foundCppProg & _prgFlags %++ "-std=gnu99")
-        ]
-
+  cpp <- findProgram "Cmm preprocessor" progOpt [] <|> pure (programFromOpt progOpt (prgPath $ ccProgram cc) [])
   cmmCppSupportsG0 <- withTempDir $ \dir -> do
     let conftest = dir </> "conftest.c"
     writeFile conftest "int main(void) {}"
@@ -181,14 +175,9 @@ findCmmCpp progOpt cc = checking "for a Cmm preprocessor" $ do
 findCpp :: ProgOpt -> Cc -> M Cpp
 findCpp progOpt cc = checking "for C preprocessor" $ do
   -- Use the specified CPP or try to use the c compiler
-  foundCppProg <- findProgram "C preprocessor" progOpt [] <|> pure (programFromOpt progOpt (prgPath $ ccProgram cc) [])
-  -- Check whether the C preprocessor needs -std=gnu99 (only very old toolchains need this)
-  Cc cpp2 <- oneOf "cc doesn't support C99" $ map checkC99Support
-        [ Cc foundCppProg
-        , Cc (foundCppProg & _prgFlags %++ "-std=gnu99")
-        ]
+  cpp <- findProgram "C preprocessor" progOpt [] <|> pure (programFromOpt progOpt (prgPath $ ccProgram cc) [])
   -- Always add the -E flag to the CPP, regardless of the user options
-  let cppProgram = addFlagIfNew "-E" cpp2
+  let cppProgram = addFlagIfNew "-E" cpp
   return Cpp{cppProgram}
 
 --------------------------------------------------------------------------------



View it on GitLab: https://gitlab.haskell.org/ghc/ghc/-/commit/3c9bcb378efe476fed312fe4e12c6a51...

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View it on GitLab: https://gitlab.haskell.org/ghc/ghc/-/commit/3c9bcb378efe476fed312fe4e12c6a51...
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Cheng Shao (＠TerrorJack)

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